After constructing some preamp circuits for electret microphones, as described in the first article in this series, I started to look at different uses for them.

First of all, I had some conventional instruments to amplify – a xylophone and a glockenspiel; secondly, I wanted to make percussion instruments from some plastic bottles.

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I had a collection of plastic bottles, which would be suitable for tuned (or semi-tuned) percussion. I sawed the ends off, leaving them at different lengths – and therefore sounding at different pitches – and prepared a framework to attach them to. This consisted of small square trays which I bought, and 2x2cm wood, which I cut to length.

I then glued the bottles to each side of the central post:

Each bottle would have an electret microphone inside. The electret elements were salvaged from part of a job lot of voice memo recorders which I bought in bulk on eBay. These were said to be non-working, but their only problem seemed to be that the coin-type batteries had run down. The electret element can be seen in position at the top of the right-hand picture below.

The electrets were to be mounted inside the plastic bottles on short lengths of rigid acrylic tubing.

The pictures below give an idea of how the electrets attach to the tubes, and the tubes attach to the instruments’ bases:

Following on from this post, I will describe the xylophone and glockenspiel which also needed an economical method of amplifying; and then installing the electronics for all the new percussion instruments.